Temperature compensated high-q lines or circuits



Sept. 26, 1939. F. A. KOLSTER 7 8 TEMPERATURE COMPENSATED HIGH-Q LINES 0R CIRCUITS File'd June 19, 1936 INVENTOR F REDERKZK A. KOLSTER Y ATTORNEY Patented Sept. 26, 1939 UNITED, STATES PATENT OFFICE ard Electric Corporation, :New York, N. Y., a corporation of Delaware 7 Application June 19, 1936; Serial No, 86,131

6 Claims. (01. 178- 44) This invention relates to low loss lines or circuits which are particularly adapted for use in conjunction with very high frequency operations, and pertains more particularly to means for as- 5 suring the stability of the line or circuit regardless of changes in temperature.

It is an object of my invention to provide in conjunction with low loss lines or circuits commonly called high-Q lines or circuits means for counteracting changes occurring in the inductance and capacity constants with a change in temperature.

The effectiveness of high-Q lines or circuits as frequency stabilizing means adapted for use 15. in conjunction with the generation of high frequency oscillations has now become generally recognized in the artof practical radio engineering. Such high-Q lines or circuits, which will hereinafter be referred to merely as high-Q lines,

are now used with considerabletsuccess in'place of piezo crystals as frequency stabilizing means, particularly where it is desired to generate ultra high frequencies at high power output rates. At these ultra high frequencies, which may range from about 7 to 500 megocycles for example, ity

is particularly important to make sure that the high-Q circuit will maintain substantially constant its preselected resonant frequency. Such high-Q lines are commonly of the concentric type wherein two tubular conductors are concentrically disposed one outside the other. The conductors may be of copper, aluminum or any other metal, but in any event expansion of the metal with a change in temperature takes place. The

temperature change may be brought about by heating of the line as a result of its power input as well, as from a change in the ambient temperature. The result of these temperature changes in an ordinary uncompensated line is an increase in the inductance as well as an increase in the capacitance witha resultant decrease; in the natural frequency of the line.

In accordance with my invention I prevent temperature changes from causing anysubstantial variation in the natural frequency of the line by providing an auxiliary control capacity which is adapted to be decreased with an increase in temperature, suiiiciently to compensate for the increase in inductance and capacity of the no line and thereby maintain the pre-selected frequency constant.

have been made heretofore for providing such auxiliary capacities but in accordance; with my invention an improved arrangement is provided 55-, wherebythe. choice of materials for the line and I am aware that proposals the arrangement of the compensating mechanism may be very simply and easily made.

I proposeto connect to the outer conductor of the line-at a point preferably adjacent one end, a stationary or fixed condenser plate and to 5 locate adjacent this plate and preferably in a plane substantially parallel thereto, a cooperating adjustable condenser plate; this last mentioned plate is adapted for movement relative to the portion of the inner conductor nearest to 10 the condenser plate but is fixed by means insensitive to temperature changes, to a point on the inner conductor displaced from both condenser plates. The connection between the adjustable condenser plate and the inner conductor 15 may be made by means of Invar metal or may be made through the agency of connected lengths of metals having dissmiilar coefficients of expansion so selected as to bring about the fixed relation between the adjustable condenser plate and its point of anchorage to the inner conductor;

The above mentioned and further objects and advantages of my invention and the manner of attaining them will be more fully set forth in the following description taken in conjunction 25 with the accompanying drawing;

In the drawing Fig, 1 illustrates diagrammatically in side elevation and partly in section a compensating mechanism in accordance with my invention and Fig. 2 illustrates a modified form 30 of compensating mechanism embodying the principles of my invention.

Referring more particularly to the drawing,' reference numeral I indicates generally a high- Q line having an outer conductor 2 and an inner 35 conductor 3. These are both tubular and are preferably of the same metal, for example, cop-. per or aluminum. Connected to the outer conductor 2 is an enlarged drum 4 the end of which is partially closed byv a cap 5 forming a station- 40 ary condenser plate. The cap has a centrally located aperture in which is positioned an insulating bushing 6 of Isolantite or similar insulator suitable for high frequency use. This insulator encircles the inner conductor and serves to hold it in proper spaced relation with respect to the outer conductor. A set screw 1 holds the insulator in proper position. The elements 2, 4 and 5 may be held together by means of screw joints as shown or by any other suitable means. Located adjacent to the stationary condenser plate 5 forming the end of the drum 4 is an adjustable cooperating condenser plate 8 which encircles the inner conductor 3 but has freedom of movement with respect thereto which is perusually being relatively expensive.

mitted by an opening 9 in the plate. A cylindrical sleeve 10 of material having a low coemcient of thermal expansion, such as Invar, is fixed to the plate 8 and serves as a connecting means establishing the position of plate 8 with respect to a collar ll fixedly connected to the inner conductor 3 at a point remote from both of the condenser plates, as shown on the drawing. This sleeve is adapted for an adjustment longitudinally of the inner conductor, being held in position by set screw [2, so that the initial capacity between the condenser plates 8 and 5 may be made any desired value. It is desirable to plate the outer surface of the sleeve with -a low resistance metal, e. g. copper or silver, in order to reduce its electrical resistance to a value comparable'with that of the material used in constructing the line. Alternatively connecting wires or pigtails of copper or some other good conductor maybe connected between the plate 8 and the collar 10.

While the collar II has been shown as larger than the conductor 3 it might be made slightly smaller than the inner conductor, the latter being reduced in diameter so that the Invar sleeve would form, ineffect, a smooth continuation of the inner conductor without any change of diameter, or in this latter type of arrangement the collar ll might be omitted and the Invar metal sleeve be connected at its free end to a reduced portion of the inner conductor 3, sufiicient clearance being left between the inner conductor and the remainder of the Invar sleeve to permit relative motion in spite of thermal expansion.

Fig. 2 illustrates another embodiment of the invention wherein corresponding parts are indicated by similar reference numerals. In this case the plate 8 is fixed to the collar H by means of two tubular sleeves l3 and [4 of, for example, copper and aluminum respectively, which are interconnected at their outer. ends by an annular ring l5. The relativelengthsand coefficients of expansion ofthe two sleeves l3 and I4 is such that the distance between the plate 8 and the collar ll. does not vary with a change in temperature, the effect being the same as when the Invar connection of Fig. 1 is used.

'The construction of Fig. 2 has the advantage that it avoids the use of Invar or other material of a low coefficient of expansion, such materials In connection with the structure just described the sleeves I3 and I4 may, as in the case of Fig. 1, be made of relatively small diameter and be connected to the inner conductor ata point of reduced diam-,

eter so that the entire compensating mechanism will not exceed the diameter of the inner conductor, thereby leaving a smooth surface from the conductor to the condenser plate. In the drawing the parts have been shown in widely spaced relation for the sake of clarity. Obviously the sleeves l3 and I4 need not be widely spaced as shown but may instead be placed subover a wide range of temperatures provided the following conditions are carried out:

where a and b are respectively the distances from the plate 5 to plate 8 and from plate 5 to collar II as shown in the drawing, A is the ratio of the capacitance of the line to the capacitance formed by the plates 5 and 8 and where B is the ratio of all extraneous capacitances to the capacitance formed by plates 5 and 8. Referring to Fig. 2, where the outer and inner conductors are copper, the outer sleeve I3 is copper and the inner sleeve [4 is aluminum, the previously mentioned requirement that p be constant will be carried out where m=3p, p being the distance from plate 8 to collar I I, and m the distance from collar II to ring l5 as shown in the drawing.

Other material having a greater coefficient of linear expansion than copper may be used for .the sleeve l4 instead of aluminum in which case the equation just given would be modified accordingly. For example, if zinc were used in place of aluminum for the sleeve M, the following equation should be used: m=1.272p.

A compensating mechanism constructed in accordance with the fundamental formula first mentioned assures the counteraction of the increase in inductanceand capacity of the high-Q line which follows from an increase in temperature, thereby insuring that the natural frequency of the line will remain substantially constant in spite of temperature changes. The same remarks apply to the specific type coming under the formula second mentioned. In constructing a device of this character the spacing between the condenser plates 5 and 8 will have to be selected with the proper regard for the operating potential to insure against sparking between the plates, thisdistance being given as d in the formula, and the distance a must be selected accordingly to have the proper ratio. In the ordinary installation the relationships will be such that the expansion of plate 8 with a change in temperature maybe disregarded.

'While Ihave described particular embodiments of my invention for the purpose of illustration it should be understood that various modifications and adaptations thereof occurring to one skilled in the art may be made within the spirit of the invention as set forth in the following claims:

What I claim is:

1. A temperature compensated line section comprising a pair of concentric conductors subject to thermal expansion, a first condenser plate connected to the outer conductor and fixed with respect to one point of the inner conductor, a second condenser plate, and means for holding said second condenser plate adjacent to said one point of the inner conductor but in fixed relation to a predetermined intermediate other point of said inner conductor, comprising an element the efiective'length of which is independent of temperature variations, the distance between said two points being such that the relative motion of the condenser plates produced by the expansion of the inner conductor between said points counteracts frequency variations caused by the change of inductance and capacity of said line resulting from the thermal expansion thereof.

2. A temperature compensated line section comprising a pair of concentric conductors subject to thermal expansion, a first condenser plate connected to the outer conductor, a second condenser plate, and means for connecting said second condenser plate to said inner conductor at a point spaced from each of said condenser plates in such manner thatupon a change in temperature the expansion of the portion of saidinner conductor between said point and the plane of said first con- 15 denser plate, in conjunction with the expansion of said means for connecting causes a change in the capacity between said plates counteracting variations in natural frequency which are caused by the change of inductance and capacity of said line resulting from the thermal expansion thereof.

3. A temperature compensated line section comprising a pair of concentric conductors subject to thermal expansion, a first condenser plate fixed to the outer conductor, a second condenser plate, means for fixing said second condenser plate to said inner conductor at a point remote from each of said condenser plates, comprising a pair of concentric sleeves, the inner one of which is shorter than the outer one but has a higher coefijcient of thermal expansion than the outer sleeve so that the total changes in length of the two sleeves are equal, means for connecting said two sleeves together at one end, and means for attaching the other ends of the sleeves to said second plate and to said inner conductor at said point, whereby the distance between said second condenser plate and said point is maintained constant and independent of temperature changes.

4. A temperature compensated line section comprising a pair of concentricconductors subject to thermal expansion, an enlarged drum attached to the end of the outer conductor, a closure for the end of the drum forming a first condenser plate, said closure having an opening therein through which the inner conductor projects, an insulating [bushing within said opening for holding said closure in proper spaced relation with respect to said inner conductor, an annular plate encircling said inner conductor and forming a second condenser plate, a collar fixed to said inner conductor at a \point remote from each of said condenser plates and means for holding said second condenser plate in fixed relation to said collar independent of temperature changes.

5. A temperature compensated line section comprising a pair of concentric conductors subject to thermal expansion, an enlargeddrum' attached to the end of the outer conductor, a closure for the end of the drum forming a first condenser plate said closure having anopening therein through which the inner conductor projects, an insulating bushing within said opening for holding said closure in proper spaced relation with respect tosaid inner conductor, an annular plate encircling said inner conductor and forming a second condenser plate, a collar fixed to said inner conductor at a point remote from each of said condenser plates and means for holding said second condenser plate in fixed relation to said collar independent of temperature changes comprising a length of material having a low coefiicient of thermal expansion.

6. A temperature compensated line section comprising a pair of concentric conductors subject to thermal expansion, an enlarged drum attached to the end of the outer conductor, a closure for the end of the drum forming a first condenser plate said closure having an opening therein through which the inner conductor projects, an insulating bushing within said opening for holding said closure in proper spaced relation with respect to said inner conductor, an annular plate encircling said inner conductor and forming a second condenser plate, a collar fixed to said inner conductor at a point remote from each of said condenser plates and means for holding said second condenser plate in fixed relation to said collar independent of temperature changes, comprising a pair of concentric sleeves the inner sleeves having a higher coeifiicient of thermal expansion than the outer sleeve.

FREDERICK A. KOLSTER,,- 

